Ariane 5 > Overview
As the world's reference for heavy-lift launchers, Ariane 5 carries payloads weighing more than 10 metric tons to geostationary transfer orbit (GTO) and over 20 metric tons into low-Earth orbit (LEO) – with a high degree of accuracy mission after mission.
This performance ensures that Ariane 5 will be able to loft the heaviest spacecraft in production or on the drawing boards, and enables Arianespace to match up most telecommunications satellites for highly efficient dual launches – a capability that has been proven by the company in Ariane missions since the 1980s.
Arianespace operates two versions of the Ariane 5, ensuring high-quality vehicles that are standardized and repeatable in production, and delivered ready for launch.
Ariane 5 ECA is the heavy-lift workhorse for missions to GTO, and usually carries two telecommunications satellite payloads. It is powered during the initial flight phase by a cryogenic core stage and two solid rocket boosters, followed by the use of a cryogenic upper stage for orbital injection of the payload.
The Ariane 5 ES is tailored for low-Earth orbit missions with the Automated Transfer Vehicle – a resupply spacecraft for the International Space Station that weighs more than 19,000 kg. at liftoff. This Ariane 5 version also is capable of lofting satellites for Europe’s new Galileo space-based navigation system. Its primary difference from the Ariane 5 ECA configuration is the use of a storable propellant upper stage, which can perform multiple burns to deploy payloads into the desired orbit.
Main cryogenic stage
As the central element of Ariane 5, the core cryogenic stage serves as one of the launcher's key propulsion systems.
It carries a propellant load of 132.27 metric tons of liquid oxygen and 25.84 metric tons of liquid hydrogen to feed the stage's Vulcain main engine.
The Vulcain burns for just under 600 seconds, providing up to 116 metric tons of thrust in vacuum.
The stage has an overall length of 30.5 meters from the Vulcain main engine's nozzle to the forward (upper) skirt.
Its dry mass is 12.2 metric tons, and the liftoff mass with its load of cryogenic propellant is 170.3 metric tons.
After completing its propulsive mission, the empty stage is commanded to reenter the atmosphere for an ocean splashdown.
Solid booster stage
Ariane 5 utilizes two solid boosters, each standing more than 30 meters tall with 237.8 metric tons of propellant. 
The boosters are ignited on the launch pad once the main cryogenic stage's Vulcain engine has stabilized its thrust output.
They deliver more than 90 percent of the launcher's total thrust at the start of flight and burn for 130 sec. before they are separated over a designated zone of the Atlantic Ocean.
The booster stage’s solid rocket motor is made up of three segments: the 11.1-meter-long aft (lower) segment, which is loaded with 106.7 metric tons of propellant; the center segment, with a length of 10.17 meters and 107.4 metric tons of propellant; and the 3.5-meter-long forward (upper) segment, loaded with 23.4 metric tons of propellant.
A propellant mix of 68 percent ammonium perchlorate (oxidizer), 18 percent aluminum (fuel), and 14 percent polybutadiene (binder) is used in the solid rocket motors.
The combustion process is initiated by a pyrotechnic device, and the solid propellant burns at a radial velocity (from the center outward) of approximately 7.4 mm/sec.
Flight control is provided by the boosters' movable nozzle, which is driven by hydraulically-controlled servoactuators.
ESC-A cryogenic upper stage and vehicle equipment bay
The Ariane 5 ECA launcher version utilizes the ESC-A cryogenic upper stage, which is powered by an HM7B engine. This reliable engine – which also served in the upper stage on Arianespace’s legendary Ariane 4 family of launchers – develops 67 kN maximum thrust in vacuum, and is turbopump-fed and regeneratively cooled. Its thrust chamber is fed by two pumps (liquid hydrogen and liquid oxygen) driven by a gas generator, a common turbine and a gearbox.
During the powered flight, the attitude control in pitch and yaw is ensured by gimballing of the engine’s nozzle, while gaseous hydrogen thrusters are used for roll control. During the ballistic phase, roll, pitch and yaw control uses clusters of gaseous hydrogen thrusters, while gaseous oxygen thrusters also are employed for longitudinal boosts.
As part of streamlining for the Ariane 5’s assembly process, its ESC-A upper stage and the launcher’s vehicle equipment bay are pre-integrated in Europe by prime contractor EADS Astrium. This combined “upper composite” is installed as a single unit atop the Ariane 5’s core cryogenic stage in the Spaceport’s Launcher Integration Building, optimizing the preparation workflow and accelerating Arianespace’s mission rate for its workhorse vehicle.
The Ariane 5’s vehicle equipment bay integrates the guidance, stage sequencing, telemetry, tracking and safety systems. Two redundant ring laser gyroscopes are used for inertial reference and guidance during the mission.
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